Channel equalization for wireless communication devices

ABSTRACT

A wireless communication device is described. The wireless communication device includes a receiver. The receiver is configured to determine a time-domain sample of a single carrier based on a received signal. The receiver is also configured to determine an estimated value based on the time-domain sample. The receiver is further configured to perform slicing based on the estimated value to produce a sliced value. The receiver is additionally configured to adapt a frequency-domain coefficient based on the estimated value and the sliced value. The receiver is also configured to perform channel equalization based on the frequency-domain coefficient.

FIELD OF DISCLOSURE

The present disclosure relates generally to electronic devices. Morespecifically, the present disclosure relates to channel equalization forwireless communication devices.

BACKGROUND

In the last several decades, the use of electronic devices has becomecommon. In particular, advances in electronic technology have reducedthe cost of increasingly complex and useful electronic devices. Costreduction and consumer demand have proliferated the use of electronicdevices such that they are practically ubiquitous in modern society. Asthe use of electronic devices has expanded, so has the demand for newand improved features of electronic devices. More specifically,electronic devices that perform new functions and/or that performfunctions faster, more efficiently, or with higher quality are oftensought after.

Some electronic devices (e.g., cellular phones, smartphones, laptopcomputers, etc.) communicate with other electronic devices. For example,electronic devices may transmit and/or receive radio frequency (RF)signals to communicate. Improving electronic device communication may bebeneficial.

SUMMARY

A wireless communication device is described. The wireless communicationdevice includes a receiver. The receiver is configured to determine atime-domain sample of a single carrier based on a received signal. Thereceiver is also configured to determine an estimated value based on thetime-domain sample. The receiver is further configured to performslicing based on the estimated value to produce a sliced value. Thereceiver is additionally configured to adapt a frequency-domaincoefficient based on the estimated value and the sliced value. Thereceiver is also configured to perform channel equalization based on thefrequency-domain coefficient.

To determine the time-domain sample, the receiver may be configured totransform the received signal to produce a frequency-domain sample. Thereceiver may also be configured to perform an initial channelequalization on the frequency-domain sample to produce an equalizedsample. The receiver may further be configured to inverse transform theequalized sample to produce the time-domain sample of the singlecarrier.

The receiver may be configured to estimate a channel based on a receivedreference signal. The receiver may also be configured to initialize thefrequency-domain coefficient based on the estimated channel. Thereceiver may further be configured to perform the initial channelequalization based on the initialized frequency-domain coefficient.

The receiver may be configured to perform the slicing in response to adetermination of a channel condition. The channel condition may be basedon at least one of Doppler spread, delay spread, or wirelesscommunication device movement.

The receiver may be configured to initialize a time-domain coefficientto zero. The receiver may be configured to adapt a time-domaincoefficient based on the estimated value and the sliced value.

The receiver may be configured to determine a feedback value based on atime-domain coefficient. The receiver may also be configured todetermine the estimated value based on the feedback value and thetime-domain sample.

The receiver may be configured to determine the estimated value as adifference between the feedback value and the time-domain sample. Thetime-domain sample may be based on a single-carrier frequency-divisionmultiple access (SC-FDMA) signal.

A method performed by a wireless communication device is also described.The method includes determining a time-domain sample of a single carrierbased on a received signal. The method also includes determining anestimated value based on the time-domain sample. The method furtherincludes performing slicing based on the estimated value to produce asliced value. The method additionally includes adapting afrequency-domain coefficient based on the estimated value and the slicedvalue. The method also includes performing channel equalization based onthe frequency-domain coefficient.

A non-transitory tangible computer-readable medium storingcomputer-executable code is also described. The computer-readable mediumincludes code for causing a processor to determine a time-domain sampleof a single carrier based on a received signal. The computer-readablemedium also includes code for causing the processor to determine anestimated value based on the time-domain sample. The computer-readablemedium further includes code for causing the processor to performslicing based on the estimated value to produce a sliced value. Thecomputer-readable medium additionally includes code for causing theprocessor to adapt a frequency-domain coefficient based on the estimatedvalue and the sliced value. The computer-readable medium also includescode for causing the processor to perform channel equalization based onthe frequency-domain coefficient.

An apparatus is also described. The apparatus includes means fordetermining a time-domain sample of a single carrier based on a receivedsignal. The apparatus also includes means for determining an estimatedvalue based on the time-domain sample. The apparatus further includesmeans for performing slicing based on the estimated value to produce asliced value. The apparatus additionally includes means for adapting afrequency-domain coefficient based on the estimated value and the slicedvalue. The apparatus also includes means for performing channelequalization based on the frequency-domain coefficient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one example of a wirelesscommunication device in which systems and methods for channelequalization for wireless communication devices may be implemented;

FIG. 2 is a flow diagram illustrating an example of a method for channelequalization;

FIG. 3 is a flow diagram illustrating an example of a method forinitializing decision feedback equalization from a reference signal;

FIG. 4 is a block diagram illustrating an example of functions and/orblocks for performing channel equalization in accordance with some ofthe configurations described herein;

FIG. 5 is a flow diagram illustrating another example of a method forchannel equalization;

FIG. 6 is a diagram illustrating an example of a subframe of symbols fora single-carrier frequency-division multiple access (SC-FDMA) cellularvehicle-to-everything (C-V2X) waveform;

FIG. 7 is a block diagram illustrating a more specific example of awireless communication device in which systems and methods for channelequalization for wireless communication devices may be implemented;

FIG. 8 is a diagram illustrating an example of a vehicle in motion on aroad;

FIG. 9 is a diagram illustrating an example of a smartphone in motionrelative to a base station; and

FIG. 10 illustrates certain components that may be included within anelectronic device configured to implement various configurations of thesystems and methods disclosed herein for channel equalization forwireless communication devices.

DETAILED DESCRIPTION

Some configurations of the systems and methods disclosed herein relateto channel equalization for wireless communication devices. Mobiledevices may be wireless communication devices that may communicate withother devices using radio frequency (RF) signals in mobile scenarios. Inhigh mobility scenarios, an error floor occurs due to high Dopplerspread, which may cause significant channel estimation error (e.g.,inter-symbol interference (ISI)). Some examples of high mobilityscenarios include some cellular vehicle-to-everything (C-V2X) scenarios.For instance, significant channel estimation errors occur whenattempting to communicate with a vehicle that is moving at a relativelyhigh speed. Some approaches to improving communication in high mobilityscenarios may include adding reference symbols (e.g., demodulationreference signal (DMRS) symbols). In some cases, adding more referencesymbols may be insufficient to provide reliable communication. Forinstance, a 100% error rate may occur for a C-V2X Release 15 pilotpattern (with reference symbols 2, 5, 8, and 11, for example) and highmodulation and coding schemes (MCSs) in 16 quadrature amplitudemodulation (16-QAM) with a Doppler shift of 2700 hertz (Hz).Additionally, a 100% error rate may occur for some scenarios in release16 C-V2X that use an orthogonal frequency-division multiplexing (OFDM)waveform.

Some configurations of the techniques described herein improve detectionin high mobility scenarios. For example, some of the techniquesdescribed herein use additive decision feedback equalization in coherentsingle-carrier frequency-division multiple access (SC-FDMA) forhigh-mobility scenarios. Some configurations of the techniques describedherein may improve coverage and/or throughput. Some configurations ofthe techniques described herein may improve a block error rate (BLER)from 100% to 0% for some high mobility and/or high MCS scenarios.

Some configurations of the techniques described herein utilize additivedecision feedback equalization (DFE). For example, DFE feed forward isinitialized with a frequency domain channel estimation. In someapproaches, feedback is initialized with zeros in a length of delayspread or cyclic prefix (CP). For instance, feedback may not be appliedwhen equalization is relatively accurate. In some examples, DFE is addedin a receiver to compensate for channel estimation error only forhigh-mobility scenarios.

Some configurations of the techniques described herein perform feedforward. After the feed forward, for example, an inverse transform(e.g., inverse discrete Fourier transform (IDFT)) may producetime-domain samples. The time-domain samples may be subtracted withfeedback samples and passed through a slicer (e.g., hard slicer) with anestablished constellation. For instance, hard slicing is performed onestimated values from the subtraction. In some configurations, anadaptive procedure (e.g., normalized least mean squares (NLMS)procedure) is utilized to adapt (e.g., determine, update, etc.)coefficients (e.g., weights). For example, the coefficients are adaptedwith a configurable step size. Some configurations of the techniquesdescribed herein may determine a channel condition to determine whetherto activate adaptive decision feedback equalization. For instance, someconfigurations of the techniques utilize a Doppler detector to estimateDoppler spread. If the Doppler spread satisfies a threshold, forinstance, adaptive decision feedback equalization is activated. Asdescribed above, relatively high Doppler shift may cause significantchannel estimation errors. Some of the techniques described herein maybe useful for scenarios with high Doppler shift.

Various configurations are now described with reference to the Figures,where like reference numbers may indicate functionally similar elements.The systems and methods as generally described and illustrated in theFigures herein could be arranged and designed in a wide variety ofdifferent configurations. Thus, the following more detailed descriptionof several configurations, as represented in the Figures, is notintended to limit scope, as claimed, but is merely representative of thesystems and methods.

FIG. 1 is a block diagram illustrating one example of a wirelesscommunication device 102 in which systems and methods for channelequalization for wireless communication devices may be implemented. Thewireless communication device 102 (e.g., mobile device) is a device orapparatus for transmitting and/or receiving RF signals. Examples of thewireless communication device 102 include user equipments (UEs),smartphones, tablet devices, computing devices, computers (e.g., desktopcomputers, laptop computers, etc.), televisions, cameras, virtualreality devices (e.g., headsets), vehicles (e.g., semi-autonomousvehicles, autonomous vehicles, etc.), robots, aircraft, drones, unmannedaerial vehicles (UAVs), healthcare equipment, gaming consoles, Internetof Things (IoT) devices, etc. The wireless communication device 102includes one or more components or elements. One or more of thecomponents or elements may be implemented in hardware (e.g., circuitry)or a combination of hardware and instructions (e.g., a processor withsoftware and/or firmware stored in memory).

In some configurations, the wireless communication device 102 includes areceiver 106 and/or one or more antennas 104. In some configurations,the wireless communication device 102 includes one or more othercomponents and/or elements. For example, the wireless communicationdevice 102 may include a transmitter, memory, processor, and/or display(e.g., touchscreen), etc.

The receiver 106 enables the wireless communication device 102 toreceive signals from one or more other electronic devices. For example,the receiver 106 provides an interface for wireless communications. Insome configurations, the receiver 106 may be coupled to one or moreantennas 104 for receiving signals. The receiver 106 may be circuitryconfigured to perform one or more functions. For example, the receiver106 may include one or more integrated circuits with circuit components(e.g., transistors, resistors, capacitors, etc.). For instance, thereceiver 106 includes one or more switches, filters, amplifiers,converters, and/or processors, etc. In some configurations, the receiver106 may be included in an RF front-end and/or may include an RFfront-end.

The antenna(s) 104 may capture one or more signals (e.g.,electromagnetic signals, RF signals, wireless signals, referencesignals, data signals, etc.) and provide the signal(s) to the receiver106. The receiver 106 may convert the signal(s) or portions of thesignal(s) into data (e.g., bits). For example, the receiver 106 performsfiltering, analog-to-digital conversion, transformation (e.g.,transformation to the frequency domain and/or transformation to the timedomain), demapping (e.g., subcarrier demapping), equalization,demodulation, detection, and/or decoding, etc. In some configurations,the receiver 106 executes instructions to perform the one or morefunctions. In some configurations, the receiver 106 includes one or morefunctionalities that are structurally implemented as hardware (e.g.,circuitry). In some configurations, the receiver 106 includes a basebandprocessor, a modem, a modem processor, and/or any combination thereof.In some examples, the wireless communication device 102 and/or thereceiver 106 may be configured to perform one or more of the methods200, 300, 500, functions, and/or operations described in relation to oneor more of the Figures. In some examples, the wireless communicationdevice 102 and/or receiver 106 includes one or more of the componentsand/or elements described in relation to one or more of the Figures.

In some configurations, the receiver 106 may be an example of a SC-FDMAreceiver and/or of an orthogonal frequency-division multiplexing (OFDM)receiver. For example, some of the techniques described herein may beimplemented in a receiver. In some examples, the wireless communicationdevice 102 and/or receiver 106 may implement one or more aspects ofspecifications (e.g., 3rd Generation Partnership Project (3GPP) Release15, 3GPP Release 16, fifth generation (5G), New Radio (NR), and/orLong-Term Evolution (LTE), etc.). For instance, one or more of thetechniques described herein may be utilized for future specificationreleases. In some configurations, the receiver 106 receives signals froma network or networks. For instance, the receiver 106 may receivesignals from a cellular network, wireless local area network (WLAN),and/or personal area network (PAN), etc.

In some configurations, the receiver 106 receives signals (e.g.,Physical downlink packets, downlink control information, referencesignals, Physical Sidelink Shared Channel (PSSCH) information, PhysicalSidelink Control Channel (PSCCH) information, and/or DemodulationReference Signals (DMRS), etc.) from one or more devices (e.g., basestation, evolved NodeB (eNodeB), next generation NodeB (gNB), etc.). Insome examples, one or more network devices (e.g., base stations, accesspoints, wireless communication devices, etc.) may send signalsrepresenting digital information to the wireless communication device102. In some examples, the received signal may be an SC-FDMA signal.

In some configurations, the receiver 106 includes a sample determiner108, a channel equalizer 110, an estimated value determiner 112, aslicer 114, and/or a coefficient adapter 116. One or more of thecomponents and/or elements (e.g., sample determiner 108, channelequalizer 110, estimated value determiner 112, slicer 114, and/orcoefficient adapter 116) may be implemented in hardware (e.g.,circuitry) or in a combination of hardware and instructions (e.g.,processor with software and/or firmware).

The sample determiner 108 may determine one or more time-domain samplesbased on a received signal. For example, the sample determiner 108determines a time-domain sample of a single carrier based on a receivedsignal. In some configurations, to determine the time domain sample(s),the receiver 106 (e.g., sample determiner 108) transforms the receivedsignal to produce a frequency-domain sample. For example, the sampledeterminer 108 performs a Fourier transform (e.g., fast Fouriertransform (FFT), discrete Fourier transform, etc.) to produce one ormore frequency-domain samples. In some configurations, performing an FFTon one or more received samples to produce one or more frequency-domainsamples may be performed in accordance with Equation (1).

$\begin{matrix}{Y_{i} = {\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}{y_{n}e^{{- j}2{\pi{(\frac{ni}{N})}}}}}}} & (1)\end{matrix}$In Equation (1), y_(n) is a received sample with index n (e.g., receivedsamples in the time domain, (y₀, y₁, . . . , y_(N-1)), etc.), N is theFFT (e.g., discrete Fourier transform (DFT)) size, Y_(i) is afrequency-domain sample with index i, j is √{square root over (−1)}, ande is Euler's number. For instance, Y_(i) may be a DFT output in thefrequency domain.

In some examples, to determine the time-domain sample(s), the receiver106 (e.g., sample determiner 108, channel equalizer 110) performs achannel equalization on one or more frequency-domain samples to produceone or more equalized samples. For instance, the sample determiner 108may multiply the frequency-domain samples by correspondingfrequency-domain coefficients (e.g., feed-forward coefficients,(G_(ff,0), G_(ff,1), . . . , G_(ff,N−1)), etc.) to produce the equalizedsamples.

In some examples, to determine the time-domain sample(s), the receiver106 (e.g., sample determiner 108) inverse transforms the equalizedsample to produce a time-domain sample (of the single carrier, forexample). For instance, the wireless communication device 102 (e.g.,sample determiner 108, channel equalizer 110) may perform the channelequalization and inverse transform the equalized sample(s) to producethe time-domain sample(s) in accordance with Equation (2).

$\begin{matrix}{z_{n} = {\frac{1}{M}{\sum\limits_{m = 0}^{M - 1}{Y_{m}G_{{ff},m}e^{j2{\pi{(\frac{nm}{M})}}}}}}} & (2)\end{matrix}$In Equation (2), Y_(m) is a frequency-domain sample with index m (e.g.,Y_(i) from Equation (1), (Y₀, Y₁, . . . , Y_(M-1)), etc.), M is theinverse transform (e.g., inverse fast Fourier transform (IFFT), inversediscrete Fourier transform (IDFT)) size, and z_(n) is a time-domainsample with index n (e.g., (z₀, z₁, . . . , z_(M-1))). In some examples,the time-domain sample may be based on an SC-FDMA signal.

In some configurations, the receiver 106 (e.g., sample determiner 108,channel equalizer 110) may perform an initial channel equalization onthe frequency-domain sample to produce an equalized sample. For example,the receiver 106 (e.g., sample determiner 108, channel equalizer 110)estimates a channel based on a received reference signal. For instance,the receiver 106 may receive a DMRS symbol that may be utilized toestimate the channel. The estimated channel may indicate one or moreinitial frequency-domain coefficients. In some examples, the receiver106 (e.g., sample determiner 108, channel equalizer 110) performs linearequalization (e.g., minimum mean square error (MMSE) linearequalization) to produce the initial frequency-domain coefficient(s).

In some examples, the receiver 106 (e.g., sample determiner 108, channelequalizer 110) initializes one or more frequency-domain coefficientsbased on the estimated channel. For example, the frequency-domaincoefficients for channel equalization are set to the initialfrequency-domain coefficients. The initialized frequency-domaincoefficients may be utilized to perform the initial channelequalization. For instance, the receiver 106 (e.g., sample determiner108, channel equalizer 110) performs the initial channel equalizationbased on the initialized frequency-domain coefficient(s). For example,the initial channel equalization and inverse transform may be performedto determine (initial) time-domain samples.

In some configurations, the receiver 106 (e.g., estimated valuedeterminer 112) determines an estimated value based on a time-domainsample. For example, the estimated value determiner 112 may determine adifference between the time-domain sample and one or more feedbackvalues to determine an estimated value. A feedback value may be based onone or more previous sliced values and/or one or more time-domaincoefficients. For example, a feedback value may be calculated as a sumof products of previous sliced values and time-domain coefficients. Insome examples, the receiver 106 (e.g., estimated value determiner 112)determines an estimated value in accordance with Equation (3).

$\begin{matrix}{{\overset{˜}{x}}_{n} = {z_{n} - {\sum\limits_{k = 1}^{K}{g_{{fb},k}{\hat{x}}_{n - k}}}}} & (3)\end{matrix}$In Equation (3), {circumflex over (x)}_(n) is a sliced value with indexn, K is a parameter (e.g., Doppler spread, cyclic prefix, or anothervalue), g_(fb,k) is a time-domain coefficient, Σ_(k=1)^(K)g_(fb,k){circumflex over (x)}_(n-k) is a feedback value, and {tildeover (x)}_(n) is an estimated value with index n. In some examples, oneor more estimated values may be utilized for further receptionoperations. For instance, one or more estimated values may be providedto a demodulator and/or decoder for decoding. In some examples, theestimated value(s) may be decoded to produce data (e.g., received bits).

In some configurations, the receiver 106 (e.g., estimated valuedeterminer 112) determines a feedback value (e.g., Σ_(k=1)^(K)g_(fb,k){circumflex over (x)}_(n-k)) based on one or moretime-domain coefficients (e.g., g_(fb)). For example, the receiver 106(e.g., estimated value determiner 112) may sum products of sliced valuesand time-domain coefficients to determine the feedback value. In someexamples, the receiver 106 initializes a time-domain coefficient tozero. For instance, one or more time-domain coefficients (e.g., g_(fb))may be set to zero for an initial pass or iteration. Accordingly, theestimated value may be equal to the time-domain sample for an initialpass or iteration (e.g., {tilde over (x)}_(n)=Z_(n)) in some approaches.

In some configurations, the receiver 106 (e.g., estimated valuedeterminer 112) determines an estimated value based on a feedback valueand a time-domain sample. As illustrated in Equation (3), the estimatedvalue {tilde over (x)}_(n) may be a difference between the feedbackvalue and the time-domain sample. For instance, the receiver 106 (e.g.,estimated value determiner 112) may determine the estimated value as adifference (e.g., subtraction) between the feedback value and thetime-domain sample.

In some examples, the estimated value is a soft estimate. For instance,the estimated value may be a soft decision for a received value. In someexamples, the sliced value is a hard value (e.g., hard-sliced valueand/or hard decision for a received value). In some approaches, the hardvalue is utilized for updating coefficients. In some examples, the hardvalue may not be utilized in decoding.

In some configurations, the estimated value may be expressed as given inEquations (4)-(6).

$\begin{matrix}{{\overset{˜}{x}}_{n} = {{z_{n} - {\sum\limits_{k = 1}^{K}{g_{{fb},k}{\overset{\hat{}}{x}}_{n - k}}}} = {{\overset{¯}{g}}_{d}^{H}{\overset{¯}{u}}_{d,n}}}} & (4)\end{matrix}$where

_(d)

[G _(ff,0) ,G _(ff,1) , . . . ,G _(ff,M)

_(fb,1) , . . . ,g _(fb,K)]^(T)  (5)and

$\begin{matrix}{{\overset{¯}{u}}_{d,n}\overset{\Delta}{=}\lbrack {{\frac{1}{M}Y_{0}},{\frac{1}{M}Y_{1}e^{j2{\pi{(\frac{n}{M})}}}},\ldots\mspace{14mu},{\frac{1}{M}Y_{M - 1}e^{j2{\pi{(\frac{n{({M - 1})}}{M})}}}},{{- {\hat{x}}_{{n - 1},\ldots\;,}} - {\hat{x}}_{n - N_{K}}}} \rbrack^{T}} & (6)\end{matrix}$In Equations (4)-(6), g _(d) is a coefficient vector, ū_(d,n) is a valueor sample vector, H denotes a Hermitian, and T denotes transpose. Thecoefficient vector may include frequency-domain coefficients andtime-domain coefficients. As illustrated in Equations (4)-(6), anestimated value may be determined based on a product of the coefficientvector and the value vector in some approaches.

In some configurations, the receiver 106 (e.g., slicer 114) performsslicing based on the estimated value to produce a sliced value. Theestimated value may be an input to the slicer 114. The slicer 114 mayutilize an established constellation to perform slicing. For instance,the wireless communication device 102 may determine the constellationwhen establishing a link with another device (e.g., base station). Insome approaches, the slicer 114 determines a nearest constellation pointto the estimated value as the sliced value (e.g., hard-sliced value,hard value, hard decision, etc.). For instance, the slicer 114determines a Euclidean distance between the estimated value and one ormore constellation points. The constellation point with the smallestdistance may be selected as the sliced value. As described above, thesliced value(s) (e.g., {circumflex over (x)}_(n-1), etc.) may beutilized to determine a feedback value for determining a subsequentestimated value.

In some configurations, the receiver 106 (e.g., coefficient adapter 116)adapts a frequency-domain coefficient and/or a time-domain coefficientbased on the estimated value and the sliced value. For example, thecoefficient adapter 116 adapts one or more frequency-domain coefficientsand/or one or more time-domain coefficients based on the estimated valueand the sliced value. For instance, the coefficient adapter 116 maydetermine a difference (e.g., subtraction) based on the sliced value andthe estimated value (e.g., a difference of the estimated value and thesliced value, a difference of conjugates, and/or {circumflex over(x)}*_(n)−{tilde over (x)}*_(n), etc.). The difference may be utilizedin an adaptive procedure to adapt (e.g., update) the frequency-domaincoefficient(s) (e.g., feed-forward coefficient(s), G_(ff)) and/or thetime-domain coefficient(s) (e.g., feedback coefficient(s), g_(fb)). Forexample, a least mean squares (LMS) approach may be utilized to updatefeed-forward and/or feedback coefficients.

In some configurations, the receiver 106 (e.g., coefficient adapter 116)adapts the frequency-domain coefficient(s) and/or the time-domaincoefficient(s) based on a cost function. An example of a cost functionis expressed as given in Equation (7).

$\begin{matrix}{{{\overset{¯}{g}}_{d,{n + 1}} - {\overset{¯}{g}}_{d,n}}}_{2}^{2} & (7)\end{matrix}$The coefficient adapter 116 may minimize the cost function to adapt thefrequency-domain coefficient(s) and/or the time-domain coefficient(s).For example, the cost function may be minimized to get a minimum step orsmallest change possible between iterations (e.g., coefficient vectorsfor n and n+1). The coefficient adapter 116 may find weights thatminimize the cost function. For example, the weights may be g _(d,n+1′)which may be optimized and/or minimized in an iterative approach. Forinstance, Equation (9), below, may be utilized to optimize and/orminimize the weights iteratively based on previous weight estimation(s),input ū*_(d,n), and/or {circumflex over (x)}_(n). In someconfigurations, the cost function may be minimized subject to aconstraint. An example of a constraint is given in Equation (8).g _(d,n+1) ^(H) ū _(d,n) ={circumflex over (x)} _(n)  (8)In Equation (8), the constraint sets a product of the coefficient vectorfor a next iteration and the value vector equal to the sliced value.

In some configurations, the frequency-domain coefficient(s) and/or thetime-domain coefficient(s) may be adapted (e.g., updated) in accordancewith Equation (9).

$\begin{matrix}{{\overset{¯}{g}}_{d,{n + 1}} = {{\overset{¯}{g}}_{d,n} + {\mu\frac{{\overset{¯}{u}}_{d,n}}{{{\overset{¯}{u}}_{d,n}_{2}^{2}}}( {{\overset{\hat{}}{x}}_{n}^{*} - {{\overset{¯}{g}}_{d,n}^{T}{\overset{¯}{u}}_{d,n}^{*}}} )}}} & (9)\end{matrix}$In Equation (9), μ is a configurable parameter and * denotes aconjugate. For example, μ may be a step size with a value between 0 and1 (e.g., 0.1). In some examples, a term of Equation (9) (e.g.,({circumflex over (x)}*_(n)−g _(d,n) ^(T)ū*_(d,n))) may correspond to adifference based on the sliced value (e.g., conjugate of the slicedvalue, {circumflex over (x)}*_(n)) and the estimated value (e.g.,conjugate of the estimated value, {tilde over (x)}*_(n), or g _(d,n)^(T)ū*_(d,n)). In some configurations, Equation (9) may be solved todetermine adapted (e.g., updated) frequency-domain coefficients and/ortime-domain coefficients for a next iteration (e.g., the coefficientvector g _(d,n+1)). For instance, Equation (9) may be an example of anupdate equation that includes the coefficient vector g _(d,n), aconfigurable parameter, and a gradient (e.g.,

$\frac{{\overset{¯}{u}}_{d,n}}{{{\overset{¯}{u}}_{d,n}}_{2}^{2}}( {{\overset{\hat{}}{x}}_{n}^{*} - {{\overset{¯}{g}}_{d,n}^{T}{\overset{¯}{u}}_{d,n}^{*}}} )$) In this example, the gradient includes a normalized value vector

$( \frac{{\overset{¯}{u}}_{d,n}}{{{\overset{¯}{u}}_{d,n}}_{2}^{2}} )$multiplied by the conjugate of the constraint ({circumflex over(x)}*_(n)−g _(d,n) ^(T)ū*_(d,n)). For instance, the value vector may benormalized in order to normalize the least mean square error (LMSE).

An example of a development of Equation (9) is given in Equation (10).

${L( {{\overset{¯}{g}}_{n + 1},{\overset{¯}{g}}_{n},\lambda} )} = {{{{{\overset{¯}{g}}_{n + 1} - {\overset{¯}{g}}_{n}}}_{2}^{2} + {\lambda( {{\overset{\hat{}}{x}}_{n} - {{\overset{¯}{g}}_{n + 1}^{H}{\overset{¯}{u}}_{n}}} )}} = {{\sum{{{{\overset{¯}{g}}_{n + 1}(k)} - {{\overset{¯}{g}}_{n}(k)}}}_{2}^{2}} + {\lambda( {{\overset{\hat{}}{x}}_{n} - {\sum{{{\overset{¯}{g}}_{n + 1}^{H}(k)}{{\overset{¯}{u}}_{n}(k)}}}} )}}}$${\nabla{L( {{\overset{¯}{g}}_{n + 1},\lambda} )}} = {\begin{bmatrix}{2{{\overset{¯}{g}}_{n + l}^{H}( { 1 ) - {2{{\overset{¯}{g}}_{n}^{H}(1)}} - {\lambda{{\overset{¯}{u}}_{n}^{H}(1)}}} }} \\* \\{{2{{\overset{¯}{g}}_{n + 1}^{H}(k)}} - {2{{\overset{¯}{g}}_{n}^{H}(k)}} - {\lambda{{\overset{¯}{u}}_{n}^{H}(k)}}} \\* \\{{\overset{\hat{}}{x}}_{n} - {\sum{{{\overset{¯}{g}}_{n + 1}^{H}(k)}{{\overset{¯}{u}}_{n}(k)}}}}\end{bmatrix} = {\begin{bmatrix}0 \\0 \\0 \\0 \\0\end{bmatrix}\begin{bmatrix}{{{\overset{¯}{g}}_{n + 1}^{H}(1)} = \frac{{2{{\overset{¯}{g}}_{n}^{H}(1)}} + {\lambda{{\overset{¯}{u}}_{n}^{H}(1)}}}{2}} \\{{{\overset{¯}{g}}_{n + 1}^{H}(k)} = \frac{{2{{\overset{¯}{g}}_{n}^{H}(k)}} + {\lambda{{\overset{¯}{u}}_{n}^{H}(k)}}}{2}} \\{{\hat{x}}_{n} = {\sum{\frac{{2{{\overset{¯}{g}}_{n}^{H}(k)}} + {\lambda{{\overset{¯}{u}}_{n}^{H}(k)}}}{2}{{\overset{\_}{u}}_{n}(k)}}}}\end{bmatrix}}}$${2{\overset{\hat{}}{x}}_{n}} = {{{2{\overset{¯}{g}}_{n}^{H}{\overset{¯}{u}}_{n}} + {\lambda{\overset{¯}{u}}_{n}^{H}{\overset{¯}{u}}_{n}\lambda}} = {{\frac{2}{{{\overset{¯}{u}}_{n}}_{2}^{2}}( {{\overset{\hat{}}{x}}_{n} - {{\overset{¯}{g}}_{n}^{H}{\overset{¯}{u}}_{n}}} ){{\overset{¯}{g}}_{n + 1}^{H}(k)}} = {{{\overset{¯}{g}}_{n}^{H}(k)} + {\frac{{\overset{¯}{u}}_{n}^{H}(k)}{{{\overset{¯}{u}}_{n}}_{2}^{2}}( {{\overset{\hat{}}{x}}_{n} - {{\overset{¯}{g}}_{n}^{H}{\overset{¯}{u}}_{n}}} )}}}}$

A conjugate may be added to yield Equation (9).

$\begin{matrix}{{\overset{¯}{g}}_{n + 1} = {{\overset{¯}{g}}_{n} + {\mu\frac{{\overset{¯}{u}}_{n}}{{{\overset{¯}{u}}_{n}}_{2}^{2}}( {{\overset{\hat{}}{x}}_{n}^{*} - {{\overset{¯}{g}}_{n}^{T}{\overset{¯}{u}}_{n}^{*}}} )}}} & (10)\end{matrix}$In Equation (10), L is the Lagrangian and

is the gradient operator. The gradient operator may be utilized todetermine a minimum that optimizes a minimization problem.

In some configurations, the receiver 106 (e.g., channel equalizer 110)performs channel equalization based on the frequency-domain coefficient.For example, the channel equalizer 110 utilizes the adaptedfrequency-domain coefficients to perform channel equalization for asubsequent iteration (e.g., to determine a subsequent sample). In someconfigurations, the receiver 106 may utilize the time-domaincoefficients to produce feedback for determining a subsequent estimatedvalue. For instance, the adapted (e.g., updated) time-domain values maybe utilized to produce feedback in accordance with Equation (3) (e.g.,g_(fb,1){circumflex over (x)}_(n-1), g_(fb,2){circumflex over(x)}_(n-2), . . . , g_(fb,K){circumflex over (x)}_(n-K)).

In some configurations, the wireless communication device 102 (e.g.,receiver 106) performs one or more of the techniques described herein inresponse to a channel condition and/or communication scheme. Forinstance, if a channel condition (e.g., threshold) is satisfied and/orif a particular communication scheme is being utilized, the wirelesscommunication device 102 (e.g., receiver 106) may activate DFE (e.g.,set a DFE activation flag) and/or perform one or more of the techniquesdescribed herein (e.g., slicing). For example, the receiver 106 mayperform one or more of the techniques described herein in response to adetermination of a channel condition. For instance, the receiver 106 maybe configured to perform slicing in response to the determination of thechannel condition. Examples of channel conditions include an amountand/or range of Doppler spread, delay spread, and/or wirelesscommunication device 102 movement. For instance, the wirelesscommunication device 102 (e.g., receiver 106) may include a Dopplerspread detector to detect Doppler spread. In a case that the Dopplerspread satisfies (e.g., is greater than or equal to) a Doppler spreadthreshold, the receiver 106 may perform one or more of the techniquesdescribed herein. In some examples, the wireless communication device(e.g., receiver 106) includes a delay spread detector to detect delayspread. In a case that the delay spread satisfies (e.g., is greater thanor equal to) a delay spread threshold, the receiver 106 may perform oneor more of the techniques described herein. In some examples, thewireless communication device 102 includes a motion detector (e.g.,accelerometer, global positioning system (GPS) receiver, camera, etc.)to detect wireless communication device 102 motion (e.g., speed,velocity, acceleration, etc.). In a case that the motion (e.g., speed,velocity, acceleration, etc.) satisfies (e.g., is greater than or equalto) a motion threshold, the receiver 106 may perform one or more of thetechniques described herein.

In some configurations, the receiver 106 performs one or more of thetechniques described herein in response to a communication scheme. Forexample, the receiver 106 may be configured to perform slicing inresponse to a determination of a communication scheme. Examples ofcommunication schemes or aspects of communication schemes includemodulation and coding scheme (MCS) and constellations. For instance,each MCS has a corresponding rate (which may influence DFE improvement).A constellation (e.g., binary phase shift keying (BPSK), quadraturephase shift keying (QPSK), quadrature amplitude modulation (QAM), etc.)may change DFE slicer accuracy. In some examples, the wirelesscommunication device 102 (e.g., receiver 106) performs one or more ofthe techniques described herein in response to a communication schemeand/or communication scheme aspect(s). For instance, the wirelesscommunication device 102 (e.g., receiver 106) may include a look-uptable and/or may utilize a function that maps a communication scheme tothe activation or deactivation of one or more of the techniquesdescribed herein.

As described above, the wireless communication device 102 may performone or more of the techniques described herein in response to a channelcondition (e.g., amount and/or range of Doppler spread, delay spread,and/or movement, etc.) and/or communication scheme (e.g., MCS). Forinstance, the wireless communication device 102 may include one or moresensors (e.g., motion sensor(s), accelerometer(s), global positioningsystem (GPS) receiver(s), RF receiver(s), transmitter(s),transceiver(s), camera(s), etc.) that may be utilized to detect achannel condition and/or communication scheme.

Some examples of channel conditions that may be detected and/or that maytrigger performance of one or more of the techniques described hereininclude a speed, relative speed, and/or Doppler shift. For instance, thewireless communication device 102 may determine (using accelerometer(s),GPS, speedometer(s), and/or received signal(s)) speed of the wirelesscommunication device 102, relative speed between the wirelesscommunication device 102 and another device, and/or Doppler shift. Forinstance, speed and/or Doppler shift may be estimated and/or obtainedfrom vehicle sensors. In an example, 500 kilometers per hour (kph) is arelative speed between the wireless communication device 102 and anotherdevice (e.g., between two cars traveling at 250 kph in oppositedirections). With a center frequency of 5.8 gigahertz (GHz), 500 kph inrelative speed translates to a Doppler shift of 2700 Hz. With this highDoppler shift, constellations above QPSK may have 100% BLER for somecommunication schemes and/or rates (e.g., MCS 16, 17, etc.).

In some examples, the wireless communication device 102 determineswhether the channel condition satisfies an activation condition (e.g.,threshold speed of 100 kph, 200 kph, 250 kph, 400 kph, and/or Dopplershift of 500 Hz, 1000 Hz, 2000 Hz, 2250 Hz, 2500 Hz, and/or a Dopplerspread amount, etc.) and/or whether a communication scheme (e.g., MCS16, 17, etc.) is being utilized. For instance, if the wirelesscommunication device 102 detects a speed greater than a threshold (e.g.,350 kph), a Doppler spread greater than a threshold (e.g., 2000 Hz),and/or that an MCS (e.g., MCS 16) is being used, then the wirelesscommunication device may activate one or more of the techniquesdescribed herein (e.g., DFE and/or slicing). In some examples, if adeactivation condition is met (e.g., speed less than a threshold, speedof 0 kph, etc.) the wireless communication device 102 may deactivateand/or not utilize one or more of the techniques described herein (e.g.,DFE and/or hard slicing). For instance, DFE and/or hard slicing may notbe utilized for lower rates (e.g., with BLER of approximately 10⁻¹).

FIG. 2 is a flow diagram illustrating an example of a method 200 forchannel equalization. In some examples, the method 200 is performed by awireless communication device (e.g., the wireless communication device102 described in relation to FIG. 1).

A wireless communication device may determine 202 a time-domain sampleof a single carrier based on a received signal. In some configurations,determining 202 one or more time-domain samples is performed asdescribed above in relation to FIG. 1. For example, the wirelesscommunication device receives a signal and performs a transform (e.g.,DFT), channel equalization, and an inverse transform (e.g., IDFT) toproduce the time-domain sample.

The wireless communication device may determine 204 an estimated valuebased on the time-domain sample. In some configurations, determining 204one or more estimated values is performed as described above in relationto FIG. 1. For example, the wireless communication device may subtract afeedback value from the time-domain sample to produce the estimatedvalue.

The wireless communication device performs 206 slicing based on theestimated value to produce a sliced value (e.g., hard sliced value). Insome configurations, performing 206 slicing is performed as describedabove in relation to FIG. 1. For example, the wireless communicationdevice may utilize an established constellation and determine aconstellation point that is nearest to the estimated value to producethe sliced value.

The wireless communication device adapts 208 a frequency-domaincoefficient based on the estimated value and the sliced value. In someconfigurations, adapting 208 one or more frequency-domain coefficientsbased on the estimated value and the sliced value is performed asdescribed above in relation to FIG. 1. For example, the wirelesscommunication device may determine a difference based on the estimatedvalue and the sliced value (e.g., conjugates of the estimated value andthe sliced value), which may be utilized to adapt 208 thefrequency-domain coefficient. In some examples, the wirelesscommunication device may also adapt a time-domain coefficient based onthe estimated value and the sliced value (e.g., the difference).

The wireless communication device performs 210 channel equalizationbased on the frequency-domain coefficient. In some configurations,performing 210 channel equalization based on one or morefrequency-domain coefficients is performed as described above inrelation to FIG. 1. For instance, the wireless communication device maymultiply one or more frequency-domain samples by respectivefrequency-domain coefficients to perform channel equalization.

FIG. 3 is a flow diagram illustrating an example of a method 300 forinitializing decision feedback equalization from a reference signal. Insome examples, the method 300 is performed by a wireless communicationdevice (e.g., the wireless communication device 102 described inrelation to FIG. 1). In some configurations, one or more of thefunctions, procedures, operations, etc., described in relation to FIG. 3may be combined with one or more of the functions, procedures,operations, methods, etc. described herein.

A wireless communication device may estimate 302 a channel based on areceived reference signal. In some configurations, estimating 302 thechannel is performed as described above in relation to FIG. 1. Forexample, the wireless communication device may receive a referencesignal and utilize the reference signal to determine channelcharacteristics.

The wireless communication device may initialize 304 a frequency-domaincoefficient based on the estimated channel. In some configurations,initializing 304 one or more frequency-domain coefficients is performedas described above in relation to FIG. 1. For example, the wirelesscommunication device may utilize quantities from equalizationcoefficients derived from the estimated channel as the initialfrequency-domain coefficients. For instance, the initialfrequency-domain coefficients may be equalization parameters determinedby the wireless communication device (e.g., modem). In some examples,the wireless communication device may perform linear minimum mean squareerror (LMMSE) channel estimation with a channel covariance matrix (Rhh)and a channel noise covariance matrix (Rnn) to produce the equalizationcoefficients.

The wireless communication device may transform 306 a received signal toproduce a frequency-domain sample. In some configurations, transforming306 the received signal is performed as described above in relation toFIG. 1. For example, the wireless communication device may perform aFourier transform, FFT, DFT, etc., on the received signal (e.g., samplesof the received signal in the time domain) to produce one or morefrequency-domain samples.

The wireless communication device may perform 308 an initial channelequalization on the frequency-domain sample based on the initializedfrequency-domain coefficient to produce an equalized sample. In someconfigurations, performing 308 an initial channel equalization on one ormore frequency domain samples based on one or more initializedfrequency-domain coefficients is performed as described above inrelation to FIG. 1. For example, the wireless communication device maymultiply frequency-domain samples with the initialized frequency domaincoefficients to produce equalized samples.

The wireless communication device may inverse transform 310 theequalized sample to produce a time-domain sample. In someconfigurations, inverse transforming 310 equalized samples is performedas described above in relation to FIG. 1. For instance, the wirelesscommunication device may apply an inverse Fourier transform (e.g., IFFT,IDFT) on the equalized samples to produce time-domain samples.

FIG. 4 is a block diagram illustrating an example of functions and/orblocks for performing channel equalization in accordance with some ofthe configurations described herein. For example, FIG. 4 illustrates atransform 418, channel equalizer 420, inverse transform 422, firstsubtractor 424, slicer 426, feedback generator 428, second subtractor430, channel estimation and minimum mean square estimation (MMSE) linearequalization 436, selector 434, and coefficient adapter 432. One or moreof the functions and/or blocks described in relation to FIG. 4 may beimplemented in hardware (e.g., circuitry) or in a combination ofhardware and instructions (e.g., software and/or firmware). In someconfigurations, one or more of the functions and/or blocks described inrelation to FIG. 4 are included in the wireless communication device 102(e.g., receiver 106) described in relation to FIG. 1. In someconfigurations, the functions described in relation to FIG. 4 areperformed in accordance with one or more of the methods and/oroperations described herein.

A wireless communication device may receive a reference signal (e.g.,DMRS). The reference signal may be provided to the channel estimationand MMSE linear equalization 436. The channel estimation and MMSE linearequalization 436 estimates a channel and/or produces equalizationparameters (e.g., equalization coefficients) based on the referencesignal. In some configurations, estimating the channel and/or producingequalization parameters are performed as described above in relation toFIG. 1 and/or FIG. 3. The channel estimation and MMSE linearequalization 436 may produce a channel estimate and/or equalizationparameters, which may be provided to the selector 434.

The selector 434 determines whether to select frequency-domaincoefficients from the channel estimation and MMSE linear equalization436 or from the coefficient adapter 432. For example, the selector 434determines frequency-domain coefficients (e.g., initializesfrequency-domain coefficients) from the channel estimation and MMSElinear equalization 436 in a case that a channel condition is satisfied,in a case that a particular communication scheme is beginning to beutilized, and/or if a DFE activation flag is detected. For instance, theselector 434 may determine frequency-domain coefficients from thechannel estimation and MMSE linear equalization 436 for a firstiteration (of DFE, for instance). After the first (e.g., initial)iteration, the selector 434 determines frequency-domain coefficientsfrom the coefficient adapter 432. In some examples, the selector 434 mayreset when DFE and/or slicing is deactivated. In some examples,selecting and/or initializing frequency-domain coefficients areperformed as described in relation to FIG. 1 and/or FIG. 3. The selector434 may provide the selected and/or determined frequency-domaincoefficients to the channel equalizer 420.

A received signal may be provided to the transform 418. The transform418 transforms the received signal to produce a frequency-domainsamples. In some configurations, transforming the received signal isperformed as described in relation to FIG. 1, FIG. 2, and/or FIG. 3. Forexample, the wireless communication device may perform a Fouriertransform, FFT, DFT, etc., on the received signal to producefrequency-domain samples.

The frequency-domain samples may be provided to the channel equalizer420. For an initial iteration, the channel equalizer 420 may perform aninitial channel equalization on the frequency-domain samples based oninitialized frequency-domain coefficients from the selector 434 toproduce equalized samples. In some configurations, performing an initialchannel equalization is performed as described in relation to FIG. 1and/or FIG. 3. For iterations after the initial iteration, the channelequalizer 420 may perform channel equalization based on adaptedfrequency-domain coefficients to produce equalized samples. Forinstance, the adapted frequency-domain coefficients may be produced bythe coefficient adapter 432 and provided to the channel equalizer 420 bythe selector 434. In some configurations, performing a channelequalization for a subsequent iteration (after the initial iteration,for example) is performed as described in relation to FIG. 1 and/or FIG.2. The channel equalizer may provide the equalized samples to theinverse transform 422.

The inverse transform 422 performs an inverse transformation on theequalized samples. In some configurations, inverse transformingequalized samples is performed as described in relation to FIG. 1, FIG.2, and/or FIG. 3. For instance, the wireless communication device mayapply an inverse Fourier transform (e.g., IFFT, IDFT) on the equalizedsamples to produce time-domain samples. The time-domain samples may beprovided to the first subtractor 424. In some examples, the time-domainsamples are provided to a serial-to-parallel converter (of a wirelesscommunication device 102 and/or receiver 106, for instance), whichconverts the time-domain samples into parallel streams and provide thetime-domain samples to the first subtractor.

The first subtractor 424 subtracts one or more feedback values from oneor more time-domain samples to produce one or more estimated values. Insome configurations, determining 204 one or more estimated values isperformed as described in relation to FIG. 1 and/or FIG. 2. Theestimated value(s) may be provided to the slicer 426 and/or to thesecond subtractor 430.

The slicer 426 performs slicing (e.g., hard slicing) based on theestimated value(s) to produce one or more sliced values. In someconfigurations, performing slicing is performed as described above inrelation to FIG. 1 and/or FIG. 2. The sliced value(s) may be provided tothe second subtractor 430 and/or to the feedback generator 428.

The second subtractor 430 performs a subtraction based on the estimatedvalue(s) and the sliced value(s) to produce a difference. For instance,the second subtractor 430 may subtract a conjugate of the estimatedvalue(s) from a conjugate of the sliced value(s) to produce thedifference. The difference may be provided to the coefficient adapter.The coefficient adapter 432 adapts (e.g., updates) frequency-domaincoefficients and time-domain coefficients based on the difference of theconjugates of the estimated value and the sliced value. For instance,the coefficient adapter 432 may utilize the sliced value and theestimated value or a quantity based on the estimated value in anadaptation calculation (e.g., Equation (9)) to produce the adaptedfrequency-domain coefficients and/or adapted time-domain coefficients.In some configurations, adapting the frequency-domain coefficients andthe time-domain coefficients is performed as described in relation toFIG. 1 and/or FIG. 2. The coefficient adapter 432 may provide theadapted frequency-domain coefficients to the selector 434 and/or mayprovide the adapted time-domain coefficients to the feedback generator428.

The feedback generator 428 generates one or more feedback values basedon the sliced value and time-domain coefficients. For an initialiteration, the time-domain coefficient(s) and/or feedback value(s) maybe set to zero. For one or more subsequent iterations, the feedbackgenerator 428 may generate the feedback value(s) based on the slicedvalue(s) and/or adapted time domain coefficients. The feedback value(s)may be provided to the first subtractor 424. In some examples,generating the feedback value(s) is performed as described in relationto FIG. 1.

FIG. 5 is a flow diagram illustrating another example of a method 500for channel equalization. In some examples, the method 500 is performedby a wireless communication device (e.g., the wireless communicationdevice 102 described in relation to FIG. 1).

A wireless communication device determines 502 whether the wirelesscommunication device is in a high mobility scenario. In someconfigurations, determining 502 whether the wireless communicationdevice is in a high mobility scenario is performed as described above inrelation to FIG. 1. For example, the wireless communication device maydetermine whether the wireless communication device is in a highmobility scenario based on one or more channel conditions, communicationscheme, and/or mobility detection. In some examples, the determination502 may be a determination whether to activate slicing and/or DFE.

In a case that the wireless communication device is not in a highmobility scenario (and/or it is determined to not use slicing and/orDFE), the wireless communication device performs 504 reception withoutslicing (and/or DFE). For example, the wireless communication device mayperform reception of an SC-FDMA signal without slicing and/or DFE. Insome configurations, the wireless communication device may continue tomonitor whether the wireless communication device is entering a highmobility scenario (and/or whether to activate slicing and/or DFE).

In a case that the wireless communication device is in a high-mobilityscenario (and/or if it is determined to activate slicing and/or DFE),the wireless communication device initializes 506 a frequency-domaincoefficient based on the estimated channel. In some configurations,initializing 506 one or more frequency-domain coefficients is performedas described in relation to FIG. 1, FIG. 3, and/or FIG. 4.

The wireless communication device may initialize 508 a time-domaincoefficient to zero. In some configurations, initializing 506 one ormore frequency-domain coefficients is performed as described in relationto FIG. 1 and/or FIG. 4.

The wireless communication device may transform 510 a received signal toproduce a frequency-domain sample. In some configurations, transforming510 the received signal is performed as described above in relation toFIG. 1, FIG. 3, and/or FIG. 4.

The wireless communication device may perform 512 channel equalizationon the frequency-domain sample based on the frequency-domain coefficientto produce an equalized sample. In some configurations, performing 512channel equalization on one or more frequency domain samples based onone or more frequency-domain coefficients is performed as described inrelation to FIG. 1, FIG. 3, and/or FIG. 4.

The wireless communication device may inverse transform 514 theequalized sample to produce a time-domain sample of a single carrier(e.g., SC-FDMA carrier). In some configurations, inverse transforming514 equalized samples is performed as described above in relation toFIG. 1, FIG. 3, and/or FIG. 4.

The wireless communication device may determine 516 an estimated valuebased on the time-domain sample. In some configurations, determining 516one or more estimated values is performed as described in relation toFIG. 1, FIG. 2, and/or FIG. 4.

The wireless communication device may perform 518 slicing on theestimated value to produce a sliced value (e.g., hard sliced value). Insome configurations, performing 518 slicing is performed as describedabove in relation to FIG. 1, FIG. 2, and/or FIG. 4.

The wireless communication device may adapt 520 a frequency-domaincoefficient and a time-domain coefficient based on the estimated valueand the sliced value. In some configurations, adapting 520 one or morefrequency-domain coefficients and/or time-domain coefficients based onthe estimated value and the sliced value is performed as described inrelation to FIG. 1, FIG. 2, and/or FIG. 4.

The wireless communication device may determine 522 a feedback valuebased on the sliced value and the time-domain coefficient. In someconfigurations, determining 522 the feedback value is performed asdescribed in relation to FIG. 1 and/or FIG. 4.

The wireless communication device may determine 524 whether to continuereception using slicing (e.g., DFE). For example, the wirelesscommunication device may determine 524 whether the wirelesscommunication device is still in a high mobility scenario (e.g., whetherthe channel condition(s) are satisfied, whether a particularcommunication scheme is being used, and/or whether a mobility conditionis satisfied). In a case that it is determined to continue, the wirelesscommunication device may transform 510 a received signal (e.g.,subsequently received signal), may perform channel equalization based onadapted frequency-domain coefficients, and so on.

FIG. 6 is a diagram illustrating an example of a subframe 646 of symbols638 for an SC-FDMA C-V2X waveform. For instance, the symbols 638 may beproduced in accordance with some aspects of Release 15 specifications.In this example, some of the symbols 638 carry data 640 (e.g., PSSCHand/or PSCCH data), some of the symbols 638 carry a reference signal 642(e.g., DMRS), and one of the symbols 638 is a guard 644 symbol. Awireless communication device may utilize the reference signal 642symbols to estimate the channel, to interpolate the channel for the data640 symbols between the reference signal 642 symbols, and to extrapolatethe channel for the last data 640 symbol (symbol S₁₂). In some highmobility scenarios, this approach may be insufficient to enable accuratereception of the data 640. Adding reference signal symbols may still beinsufficient in some scenarios as described above. Some of thetechniques described herein may help to alleviate this issue byactivating DFE in high mobility scenarios.

FIG. 7 is a block diagram illustrating a more specific example of awireless communication device 748 in which systems and methods forchannel equalization for wireless communication devices may beimplemented. The wireless communication device 748 may be an example ofthe wireless communication device 102 described in relation to FIG. 1.

In some configurations, the wireless communication device 748 includesone or more antennas 750, an RF front-end (RFE) 752, a modem 754, modemprocessor 756, modem memory 758, SC-FDMA DFE instructions 760, memory762, and/or processor 764. In some configurations, the wirelesscommunication device 748 includes one or more other components and/orelements and/or may omit one or more of the components and/or elementsshown.

The RFE 752 receives signals provided by the one or more antennas 750.In some configurations, RFE 752 may include one or more switches, one ormore filters, one or more power amplifiers, one or more downconverters,and/or one or more upconverters, etc., to enable wireless communication.The RFE 752 may provide received signals to the modem 754. In someexamples, the RFE 752 and/or modem 754 is included in a transceiver.

The modem 754 includes a modem processor 756. The modem processor 756reads SC-FDMA DFE instructions 760 from the modem memory 758. TheSC-FDMA DFE instructions 760 may include instructions for performing oneor more of the functions, operations, procedures, methods, etc.,described herein. For example, the modem processor 756 executes theSC-FDMA DFE instructions 760 to perform one or more of the functionsdescribed in relation to FIG. 4 and/or methods 200, 300, 500 describedherein. For instance, the modem processor 756 may execute the SC-FDMADFE instructions 760 when the wireless communication device 748 enters ahigh-mobility scenario. The modem 754 may provide data (e.g.,demodulated and/or decoded data) to the memory 762 and/or processor 764.The memory 762 may be separate from the modem memory 758 in someconfigurations and/or the processor 764 may be separate from the modemprocessor 756 in some configurations. For example, the processor 764 maybe an application processor that may utilize the data provided by themodem.

FIG. 8 is a diagram illustrating an example of a vehicle 866 in motionon a road 868. The vehicle 866 may be an example of one or more of thewireless communication devices described herein. In this example, thevehicle 866 is proceeding in motion on a road 868 while passing a basestation 870. When the vehicle 866 is traveling with high mobility,significant Doppler shift may occur in a signal sent from the basestation 870. For instance, high mobility may cause the communicationchannel to change rapidly. Some of the techniques described herein maybe utilized to improve throughput and performance in signal receptionfor wireless communication devices (e.g., the vehicle 866) in highmobility scenarios.

FIG. 9 is a diagram illustrating an example of a smartphone 972 inmotion relative to a base station 974. The smartphone 972 may be anexample of one or more of the wireless communication devices describedherein. In this example, the smartphone 972 is proceeding in motion awayfrom the base station 974. When the smartphone 972 is traveling withhigh mobility (e.g., in a vehicle or aircraft), significant Dopplershift may occur in a signal sent from the base station 974 and/or in asignal sent from the smartphone 972. For instance, high mobility maycause the communication channel to change rapidly. Some of thetechniques described herein may be utilized to improve throughput andperformance in signal reception for wireless communication devices(e.g., the smartphone 972) in high mobility scenarios. Some examples ofthe techniques described herein may be utilized in other high-mobilityscenarios (e.g., rapidly moving drones, rapidly moving vehiclescommunicating with each other, aircraft, etc.).

FIG. 10 illustrates certain components that may be included within anelectronic device 1076 configured to implement various configurations ofthe systems and methods disclosed herein for channel equalization forwireless communication devices. The electronic device 1076 may be anaccess terminal, a mobile station, a user equipment (UE), a smartphone,a digital camera, a video camera, a tablet device, a laptop computer, adesktop computer, an Internet of Things (IoT) device, a base station, anaccess point, a vehicle, a drone, etc. The electronic device 1076 may beimplemented in accordance with one or more of the wireless communicationdevices (e.g., wireless communication device 102) described herein.

The electronic device 1076 includes a processor 1096. The processor 1096may be a general purpose single- or multi-chip microprocessor (e.g., anARM), a special purpose microprocessor (e.g., a digital signal processor(DSP)), a microcontroller, a programmable gate array, etc. The processor1096 may be referred to as a central processing unit (CPU) and/or amodem processor. Although a single processor 1096 is shown in theelectronic device 1076, in an alternative configuration, a combinationof processors (e.g., an ARM and DSP) could be implemented.

The electronic device 1076 also includes memory 1078. The memory 1078may be any electronic component capable of storing electronicinformation. The memory 1078 may be embodied as random access memory(RAM), read-only memory (ROM), magnetic disk storage media, opticalstorage media, flash memory devices in RAM, on-board memory includedwith the processor, programmable read-only memory (PROM), erasableprogrammable read-only memory (EPROM), electrically erasable PROM(EEPROM), synchronous dynamic random-access memory (SDRAM), registers,and so forth, including combinations thereof.

Data 1082 a and instructions 1080 a may be stored in the memory 1078.The instructions 1080 a may be executable by the processor 1096 toimplement one or more of the methods described herein. Executing theinstructions 1080 a may involve the use of the data 1082 a that isstored in the memory 1078. When the processor 1096 executes theinstructions 1080, various portions of the instructions 1080 b may beloaded onto the processor 1096 and/or various pieces of data 1082 b maybe loaded onto the processor 1096. In some configurations, theinstructions 1080 may be executable to implement and/or perform one ormore of the methods 200, 300, 500, and/or one or more of the functions,procedures, and/or operations described herein.

The electronic device 1076 may also include a transmitter 1084 and areceiver 1086 to allow transmission and reception of signals to and fromthe electronic device 1076. The transmitter 1084 and receiver 1086 maybe collectively referred to as a transceiver 1088. One or more antennas1090 a-b may be electrically coupled to the transceiver 1088. Theelectronic device 1076 may also include (not shown) multipletransmitters, multiple receivers, multiple transceivers and/oradditional antennas.

The electronic device 1076 may include a digital signal processor (DSP)1092. The electronic device 1076 may also include a communicationsinterface 1094. The communications interface 1094 may allow and/orenable one or more kinds of input and/or output. For example, thecommunications interface 1094 may include one or more ports and/orcommunication devices for linking other devices to the electronic device1076. In some configurations, the communications interface 1094 mayinclude the transmitter 1084, the receiver 1086, or both (e.g., thetransceiver 1088). Additionally or alternatively, the communicationsinterface 1094 may include one or more other interfaces (e.g.,touchscreen, keypad, keyboard, microphone, camera, etc.). For example,the communication interface 1094 may enable a user to interact with theelectronic device 1076.

The various components of the electronic device 1076 may be coupledtogether by one or more buses, which may include a power bus, a controlsignal bus, a status signal bus, a data bus, etc. For the sake ofclarity, the various buses are illustrated in FIG. 10 as a bus system1098.

The term “determining” encompasses a wide variety of actions and,therefore, “determining” can include calculating, computing, processing,deriving, investigating, looking up (e.g., looking up in a table, adatabase or another data structure), ascertaining and the like. Also,“determining” can include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” can include resolving, selecting, choosing, establishing,and the like.

The phrase “based on” does not mean “based only on,” unless expresslyspecified otherwise. In other words, the phrase “based on” may describe“based only on” and/or “based at least on.”

The term “processor” should be interpreted broadly to encompass ageneral purpose processor, a central processing unit (CPU), amicroprocessor, a digital signal processor (DSP), a controller, amicrocontroller, a state machine, and so forth. Under somecircumstances, a “processor” may refer to an application specificintegrated circuit (ASIC), a programmable logic device (PLD), a fieldprogrammable gate array (FPGA), etc. The term “processor” may refer to acombination of processing devices, e.g., a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The term “memory” should be interpreted broadly to encompass anyelectronic component capable of storing electronic information. The termmemory may refer to various types of processor-readable media such asrandom access memory (RAM), read-only memory (ROM), non-volatile randomaccess memory (NVRAM), programmable read-only memory (PROM), erasableprogrammable read-only memory (EPROM), electrically erasable PROM(EEPROM), flash memory, magnetic or optical data storage, registers,etc. Memory is said to be in electronic communication with a processorif the processor can read information from and/or write information tothe memory. Memory that is integral to a processor is in electroniccommunication with the processor.

The terms “instructions” and “code” should be interpreted broadly toinclude any type of computer-readable statement(s). For example, theterms “instructions” and “code” may refer to one or more programs,routines, sub-routines, functions, procedures, etc. “Instructions” and“code” may comprise a single computer-readable statement or manycomputer-readable statements.

The functions described herein may be implemented in software orfirmware being executed by hardware. The functions may be stored as oneor more instructions on a computer-readable medium. The terms“computer-readable medium” or “computer-program product” refers to anytangible storage medium that can be accessed by a computer or aprocessor. By way of example and not limitation, a computer-readablemedium may comprise RAM, ROM, EEPROM, compact disc read-only memory(CD-ROM) or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store program code in the form of instructions and/or data structuresand that can be accessed by a computer. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk, and Blu-ray® disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers. Itshould be noted that a computer-readable medium may be tangible andnon-transitory. The term “computer-program product” refers to acomputing device or processor in combination with code or instructions(e.g., a “program”) that may be executed, processed, or computed by thecomputing device or processor. As used herein, the term “code” may referto software, instructions, code, or data that is/are executable by acomputing device or processor.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio and microwave are included in the definition oftransmission medium.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isrequired for proper operation of the method that is being described, theorder and/or use of specific steps and/or actions may be modifiedwithout departing from the scope of the claims.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein, can bedownloaded, and/or otherwise obtained by a device. For example, a devicemay be coupled to a server to facilitate the transfer of means forperforming the methods described herein. Alternatively, various methodsdescribed herein can be provided via a storage means (e.g., randomaccess memory (RAM), read-only memory (ROM), a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a devicemay obtain the various methods upon coupling or providing the storagemeans to the device.

As used herein, the term “and/or” should be interpreted to mean one ormore items. For example, the phrase “A, B, and/or C” should beinterpreted to mean any of: only A, only B, only C, A and B (but not C),B and C (but not A), A and C (but not B), or all of A, B, and C. As usedherein, the phrase “at least one of” should be interpreted to mean oneor more items. For example, the phrase “at least one of A, B, and C” orthe phrase “at least one of A, B, or C” should be interpreted to meanany of: only A, only B, only C, A and B (but not C), B and C (but notA), A and C (but not B), or all of A, B, and C. As used herein, thephrase “one or more of” should be interpreted to mean one or more items.For example, the phrase “one or more of A, B, and C” or the phrase “oneor more of A, B, or C” should be interpreted to mean any of: only A,only B, only C, A and B (but not C), B and C (but not A), A and C (butnot B), or all of A, B, and C.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes, and variations may be made in the arrangement, operation, anddetails of the systems, methods, and apparatus described herein withoutdeparting from the scope of the claims. For example, one or more of theoperations, functions, elements, aspects, etc., described herein may beomitted or combined.

Some examples of the systems and methods described herein are given asfollows. In a first example, a method includes determining a time-domainsample of a single carrier based on a received signal. The method alsoincludes determining an estimated value based on the time-domain sample.The method further includes performing slicing based on the estimatedvalue to produce a sliced value. The method additionally includesadapting a frequency-domain coefficient based on the estimated value andthe sliced value. The method also includes performing channelequalization based on the frequency-domain coefficient.

In a second example in combination with the first example, to determinethe time-domain sample, the method also includes transforming thereceived signal to produce a frequency-domain sample. The method furtherincludes performing an initial channel equalization on thefrequency-domain sample to produce an equalized sample. The methodadditionally includes inverse transforming the equalized sample toproduce the time-domain sample of the single carrier.

In a third example in combination with the second example, the methodincludes estimating a channel based on a received reference signal. Themethod also includes initializing the frequency-domain coefficient basedon the estimated channel. The method further includes performing theinitial channel equalization based on the initialized frequency-domaincoefficient.

In a fourth example in combination with any of the preceding examples,the method includes performing the slicing in response to adetermination of a channel condition. In a fifth example in combinationwith the fourth example, the channel condition is based on at least oneof Doppler spread, delay spread, or wireless communication devicemovement.

In a sixth example in combination with any of the preceding examples,the method includes initializing a time-domain coefficient to zero. In aseventh example in combination with any of the preceding examples, themethod includes adapting a time-domain coefficient based on theestimated value and the sliced value.

In an eighth example in combination with any of the preceding examples,the method includes determining a feedback value based on a time-domaincoefficient. The method also includes determining the estimated valuebased on the feedback value and the time-domain sample. In a ninthexample in combination with the eighth example, the method includesdetermining the estimated value as a difference between the feedbackvalue and the time-domain sample. In a tenth example in combination withany of the preceding examples, the time-domain sample is based on asingle-carrier frequency-division multiple access (SC-FDMA) signal.

In an eleventh example in combination with any of the precedingexamples, a wireless communication device includes a receiver that isconfigured to perform any of the methods of any of the precedingexamples. In a twelfth example in combination with any of the first tothe tenth examples, a non-transitory tangible computer-readable mediumstores computer-executable code that includes code for causing aprocessor to perform any of the methods of any of the first to tenthexamples. In a thirteenth example in combination with any of the firstto tenth examples, an apparatus includes means for performing any of themethods of any of the first to tenth examples.

What is claimed is:
 1. A wireless communication device, comprising: areceiver, wherein the receiver is configured to: determine a time-domainsample of a single carrier based on a received signal; determine anestimated value based on the time-domain sample; perform slicing basedon the estimated value and in response to a determination of a channelcondition to produce a sliced value; adapt a frequency-domaincoefficient based on the estimated value and the sliced value; andperform channel equalization based on the frequency-domain coefficient.2. The wireless communication device of claim 1, wherein to determinethe time-domain sample, the receiver is configured to: transform thereceived signal to produce a frequency-domain sample; perform an initialchannel equalization on the frequency-domain sample to produce anequalized sample; and inverse transform the equalized sample to producethe time-domain sample of the single carrier.
 3. The wirelesscommunication device of claim 2, wherein the receiver is configured to:estimate a channel based on a received reference signal; initialize thefrequency-domain coefficient based on the estimated channel; and performthe initial channel equalization based on the initializedfrequency-domain coefficient.
 4. The wireless communication device ofclaim 1, wherein the channel condition is based on at least one ofDoppler spread, delay spread, or wireless communication device movement.5. The wireless communication device of claim 1, wherein the receiver isconfigured to initialize a time-domain coefficient to zero.
 6. Thewireless communication device of claim 1, wherein the receiver isconfigured to adapt a time-domain coefficient based on the estimatedvalue and the sliced value.
 7. The wireless communication device ofclaim 1, wherein the receiver is configured to: determine a feedbackvalue based on a time-domain coefficient; and determine the estimatedvalue based on the feedback value and the time-domain sample.
 8. Thewireless communication device of claim 7, wherein the receiver isconfigured to determine the estimated value as a difference between thefeedback value and the time-domain sample.
 9. The wireless communicationdevice of claim 1, wherein the time-domain sample is based on asingle-carrier frequency-division multiple access (SC-FDMA) signal. 10.A method performed by a wireless communication device, comprising:determining a time-domain sample of a single carrier based on a receivedsignal; determining an estimated value based on the time-domain sample;performing slicing based on the estimated value and in response to adetermination of a channel condition to produce a sliced value; adaptinga frequency-domain coefficient based on the estimated value and thesliced value; and performing channel equalization based on thefrequency-domain coefficient.
 11. The method of claim 10, whereindetermining the time-domain sample comprises: transforming the receivedsignal to produce a frequency-domain sample; performing an initialchannel equalization on the frequency-domain sample to produce anequalized sample; and inverse transforming the equalized sample toproduce the time-domain sample of the single carrier.
 12. The method ofclaim 11, further comprising: estimating a channel based on a receivedreference signal; initializing the frequency-domain coefficient based onthe estimated channel; and performing the initial channel equalizationbased on the initialized frequency-domain coefficient.
 13. The method ofclaim 10, wherein the channel condition is based on at least one ofDoppler spread, delay spread, or wireless communication device movement.14. The method of claim 10, further comprising initializing atime-domain coefficient to zero.
 15. The method of claim 10, furthercomprising adapting a time-domain coefficient based on the estimatedvalue and the sliced value.
 16. The method of claim 10, furthercomprising: determining a feedback value based on a time-domaincoefficient; and determining the estimated value based on the feedbackvalue and the time-domain sample.
 17. The method of claim 16, furthercomprising determining the estimated value as a difference between thefeedback value and the time-domain sample.
 18. The method of claim 10,wherein the time-domain sample is based on a single-carrierfrequency-division multiple access (SC-FDMA) signal.
 19. Anon-transitory tangible computer-readable medium storingcomputer-executable code, comprising: code for causing a processor todetermine a time-domain sample of a single carrier based on a receivedsignal; code for causing the processor to determine an estimated valuebased on the time-domain sample; code for causing the processor toperform slicing based on the estimated value and in response to adetermination of a channel condition to produce a sliced value; code forcausing the processor to adapt a frequency-domain coefficient based onthe estimated value and the sliced value; and code for causing theprocessor to perform channel equalization based on the frequency-domaincoefficient.
 20. The computer-readable medium of claim 19, wherein thecode for causing the processor to determine the time-domain samplecomprises: code for causing the processor to transform the receivedsignal to produce a frequency-domain sample; code for causing theprocessor to perform an initial channel equalization on thefrequency-domain sample to produce an equalized sample; and code forcausing the processor to inverse transform the equalized sample toproduce the time-domain sample of the single carrier.
 21. Thecomputer-readable medium of claim 19, further comprising code forcausing the processor to initialize a time-domain coefficient to zero.22. The computer-readable medium of claim 19, further comprising codefor causing the processor to adapt a time-domain coefficient based onthe estimated value and the sliced value.
 23. An apparatus, comprising:means for determining a time-domain sample of a single carrier based ona received signal; means for determining an estimated value based on thetime-domain sample; means for performing slicing based on the estimatedvalue and in response to a determination of a channel condition toproduce a sliced value; means for adapting a frequency-domaincoefficient based on the estimated value and the sliced value; and meansfor performing channel equalization based on the frequency-domaincoefficient.
 24. The apparatus of claim 23, wherein the means fordetermining the time-domain sample comprises: means for transforming thereceived signal to produce a frequency-domain sample; means forperforming an initial channel equalization on the frequency-domainsample to produce an equalized sample; and means for inversetransforming the equalized sample to produce the time-domain sample ofthe single carrier.
 25. The apparatus of claim 23, further comprisingmeans for initializing a time-domain coefficient to zero.
 26. Theapparatus of claim 23, further comprising means for adapting atime-domain coefficient based on the estimated value and the slicedvalue.